The induction of pregnancy in female rats depends upon the copulatory behavior of the male. There are three major effects of the male's copulation: (1) His copulatory behavior, particularly the pre-ejaculatory intromissions, initiates the neuro-endocrine reflex resulting in progesterone secretion necessary for gestation. (2) The pre-ejaculatory intromission and deposition of a vaginal plug are necessary for the transport of sperm from the vagina into the uterus. (3) Post-ejaculatory copulatory stimulation, if it occurs too soon after the ejaculation, can disrupt this transport of sperm and thus interfere with fertilization and pregnancy. The research proposed in this application would continue our investigation into the mechanism and function of the behavioral influences on pregnancy in rats. We would investigate (1) the behavioral and physiological mediators of the intromissions' induction of progesterone secretion, (2) the behavioral and physiological mediators of the intromissions' effect on sperm transport, (3) the relationship of copulatory behavior to pregnancy induction in wild rats living in semi-natural conditions.